Heat insulators are applied to various products, such as precision instruments whose functions are significantly affected by temperature changes, home appliances (e.g. refrigerator), and walls and ceiling of a clean room. Conventionally, polymer foams, such as urethane foam, and glass wool are used as a heat insulator, for example. These materials are not only excellent in heat insulating properties but also lightweight and inexpensive, and therefore are used as a heat insulator in a wide range of applications. Further, a fiber reinforced plastic heat insulator formed by impregnating woven fabric or nonwoven fabric with a matrix resin (see Patent Literature 1) has been proposed as a high-strength heat insulator.
However, these heat insulators have a problem of generation of static electricity. To deal with this, heat insulators capable of preventing generation of static electricity have been proposed, such as a heat insulator formed of heat insulating layers with a metal plate interposed therebetween, and a heat insulator coated with an antistatic agent (see Patent Literature 2 and Patent Literature 3), for example. However, in the case of the heat insulator formed of heat insulating layers with a metal plate interposed therebetween, a bonding process is necessary for interposing the metal plate therebetween, and the bonding strength between the layers needs to be enhanced in addition. For these reasons, there has been a problem of an increase in the number of production processes. On the other hand, the heat insulator that uses an antistatic agent has a problem of an increase in the number of production processes since a coating process is necessary for applying the antistatic agent. Furthermore, there is an additional problem of the antistatic performance deterioration with time.